1. Field of the Invention
The present invention relates to a fluid filter. More particularly, the present invention relates to a fluid filter provided with a case body and a filter medium; the case body having an inlet and an outlet for a fluid at required positions respectively and also a holder defined therein to communicate with the inlet and outlet; the filter medium being made of a porous material having an appropriate flexibility and a uniform density and being removably housed in the holder. A fluid introduced through the inlet into the holder is allowed to pass through the filter medium where fine extraneous substances contained in the fluid are captured, and the resulting purified fluid is discharged through the outlet.
2. Description of the Related Art
As shown in FIG. 23, many of air purifiers, automobile engines, hydraulic cylinders and various kinds of other apparatuses which utilize gaseous bodies such as air and other gases or liquids such as oils (the gaseous bodies and liquids are hereinafter referred generally to as “fluids”) each have a fluid filter FL attached to a fluid inlet M1 of the apparatus M of interest so as to capture fine extraneous substances contained in the fluid and purify it. Various modes and kinds of fluid filters FL have been developed and are put into practical uses, and an example of which is shown in FIG. 24. The fluid filter FL shown in FIG. 24 is provided with a filter case (case body) 60 and a filter medium 70. The filter case 60 has an inlet 62 and an outlet 64 for a fluid at required positions respectively and also has a holder 66 defined therein to communicate with the inlet 62 and the outlet 64. The filter medium 70 is made of a porous material having an appropriate flexibility and a uniform density and is removably housed in the holder 66. A fluid introduced through the inlet 62 into the holder 66 is allowed to pass through the filter medium 70 where fine extraneous substances S contained in the fluid are captured, and the resulting purified fluid is discharged through the outlet 64.
Here, there can be suitably utilized the so-called porous materials containing a multiplicity of pores (air gaps) including synthetic resin open-cell foams such as sponge and urethane foam having open-cell structures, nonwoven fabrics, fiber assemblies, etc. as the filter medium 70. However, mode of dispersion and pressure loss vary depending on the density (size and number of air gaps) of the filter medium 70 to influence the rate of capturing extraneous substances S contained in the fluid. For example, FIG. 24 shows in structural cross-sectional view a fluid filter FL employing a filter medium 70 of a uniform density made of a low-density porous material (the so-called coarse porous material with a large air gap size), whereas FIG. 25 shows in structural cross-sectional view a fluid filter FL employing a filter medium 70 of a uniform density made of a high-density porous material (the so-called fine porous material with a small air gap size).
In the fluid filter FL shown in FIG. 24, the entire filter medium 70 is of uniformly coarse cells, so that it enjoys merits that it can reduce pressure loss and that extraneous substances S can be captured by the filter medium 70 in its entirety in a suitably dispersed state. However, it involves a problem that extraneous substances S smaller than the air gaps are not captured but pass through the filter medium 70, resulting in the failure of securely achieving purification of the fluid. On the other hand, in the fluid filter FL shown in FIG. 25, the entire filter medium 70 is of uniformly fine cells, so that it enjoys a merit that it can capture very fine extraneous substances S. However, the filter medium 70 involves problems that it increases the pressure loss and that various sizes of extraneous substances S are captured massively at the region of the filter medium 70 facing the inlet 62, so that the filter medium 70 fails to capture various sizes of extraneous substances S in its entirety and undergoes clogging soon.
Under such circumstances, there have already been proposed and put into practical uses fluid filters FL for capturing various sizes of extraneous substances S effectively, as shown in FIGS. 26 and 27, respectively. Each fluid filter FL contains a combination of a first filter medium 70A made of a low-density or coarse porous material and a second filter medium 70B made of a fine porous material which is of higher density than the first filter medium 70A to capture larger extraneous substances S and smaller extraneous substances S with the first filter medium 70A and the second filter medium 70B, respectively. In such a fluid filter FL, the first filter medium 70A and the second filter medium 70B are set in a holder 66 of a filter case 60 on the inlet 62 side and on the outlet 64 side, respectively, to enable the filter medium 70 to capture various sizes of extraneous substances S in a suitably dispersed state.
However, the use of at least two kinds of filter mediums 70(70A and 70B) of different densities requires operations of shaping each filter medium 70 into a required shape and a required size, leading to cost increase, disadvantageously. In addition, since the density of the filter medium 70 changes abruptly at the boundary between the first filter medium 70A and the second filter medium 70B, most of the extraneous substances S failed to be captured by the first filter medium 70A are captured massively on the external surface of the second filter medium 70B, so that extraneous substances S cannot be captured by each filter medium 70A(70B) throughout it. In addition, the pressure Loss cannot be minimized. Thus, the fluid filter FL still involves problems to be solved so as to improve the capturing rate.
More specifically, the conventional fluid filters FL shown in FIGS. 24 and 25 and the improved fluid filters FL illustrated in FIGS. 26 and 27 are totally devoid of the technical idea of taking advantage of the properties of the porous material that; it can easily be deformed partly by compression and that the density of the porous material can be varied freely depending on the degree of compression of the compressed region to improve the capturing rate of the filter medium 70. For example, in the fluid filters FL shown in FIGS. 24 and 25, since the filter medium 70 is designed to have an external profile conforming to the internal profile of the holder 66, as shown in FIG. 28, the filter medium 70 is not compressed at all but is housed and retained as such in the holder 66. Thus, each filter medium 70 as a whole has a uniform density, and there is a limit in improving the capturing rate, as described above. Further, in the improved fluid filters FL shown in FIGS. 26 and 27, the first filter medium 70A and the second filter medium 70B are combined and together assume an external profile conforming to the internal profile of the holder 66, as shown in FIGS. 29 and 30, so that the filter mediums 70A and 70B are not compressed at all but are housed and retained as such in the holder 66. Thus, each filter medium 70A(70B) as a whole has a uniform density, so that there is a limit in improving the capturing rate, as explained above.
Meanwhile, in the conventional fluid filters FL and the improved fluid filters FL shown in FIGS. 24 to 27, the filter medium 70 (70A, 70B) to be housed in the holder 66 is designed to conform to the spatial profile of the holder 66 so as to form substantially no clearance (space) around the filter medium 70 housed in the holder 66. Thus, the fluid introduced through the inlet 62 into the holder 66 entirely flows constantly through the filter medium 70 until it is discharged through the outlet 64, so that extraneous substances S contained in the fluid are completely captured by the filter medium 70 and are retained as trapped therein. Therefore, when the fluid filter FL is utilized for purification of a fluid containing many extraneous substances, clogging of the filter medium 70 occurs relatively soon to shorten the cycle of replacing or cleaning the filter medium 70, giving rise to problems that the filter medium 70 must be replaced or cleaned frequently and that the running cost rises.